The present invention relates generally to a method of controlling a variable geometry turbine. More particularly, but not exclusively, the present invention relates to a method for controlling a variable geometry turbocharger to affect a diesel engines exhaust gas temperature to a desired level for after-treatment systems.
After-treatment system performance is directly related to the temperature of the exhaust gas that passes through it. Designers of after-treatment systems recognize that for desired performance the exhaust gas temperature must be above a threshold temperature under all operating conditions and ambient conditions. The threshold temperature is generally recognized as being within a range of about 500° F. to about 700° F. The operation of the after-treatment system below the threshold temperature range will cause the after-treatment system to build up undesirable accumulations. The undesirable accumulations must be burnt off in a regeneration cycle to allow the after-treatment system to return to the designed performance levels. Further, prolonged operation of the after-treatment system below the threshold temperature without regeneration will disable the after-treatment system and cause the engine to become non-compliant with government regulations.
It is recognized that the exhaust gas temperatures for the majority of the operating range of a diesel engine will generally be above the desired threshold temperature. However, light load conditions and/or cold ambient temperatures often cause the exhaust gas temperature to fall below the desired threshold temperatures.
The present inventions provide a novel and non-obvious method for controlling the variable geometry turbocharger to increase the exhaust gas temperature to the desired threshold temperature for the after-treatment system.